A fibre optic technique for detecting trace amounts of nitrite compounds in
water is described. The off-line fibre optic sensor outlined here is based on
evanescent field absorption in a test solution formed by the reaction of nitrite
compounds in water with suitable chemical reagents. A short unclad portion
of a plastic clad silica fibre acts as the sensing region. The experimental
results clearly establish the usefulness of the present technique for detecting
very low concentrations of the order of 1 ppb (parts per billion) of nitrite
compounds with a large dynamic range of 1–1000 ppb. Such a high
sensitivity enables the present device to be used for measuring the nitrite
content in drinking water.